The invention relates to a vehicle wheel including a wheel rim on which multiple plate-like cover elements for temporarily closing assigned wheel side apertures are provided, wherein each cover element due to centripetal forced is shiftable along the pivot axis against the force of a restoring element and coupled with the wheel rim via a positively guiding coupling element such that the cover element is pivotal between a radially inner open position and a radially outer closed position.
The conception of modern wheel rims is subject to various, partially conflicting, demands. Beside a simple wheel rim contour, which enables an easy manufacture, a central demand is that the wheel rim allows a maximal air flow through the wheel rim to be able to optimally cool the wheel rim by the air flow when needed. Further, during a residual heating period of the brake disc at standstill, it has to be ensured that the heat can dissipate also in the absence of air flow. This results in the demand for a maximally “open” wheel rim structure.
However, for aerodynamic reasons the wheel rim should be maximally closed, to prevent air turbulences as far as possible, which are generated by openings in the wheel rim. During normal driving, an overpressure exists in the region of the underside of the vehicle, which ensures that air is pushed through the free spaces of the wheel rim. If the wheel rim was configured as closed disc, the cw-value which is included in the calculation of the air resistance of the vehicle could be improved.
In order to meet these requirements which quasi contradict one another on one hand for thermal reasons and on the other hand for aerodynamic reasons, it is known to open and close the wheel rim side openings when needed. In such systems, the plate shaped cover elements are usually pivotally supported and movable radially along the pivot axis. The cover elements are each additionally connected to the wheel rim via a force guiding coupling element. The centripetal force acting on the cover elements increases with increasing rotational speed of the wheel which causes the cover elements to move outwardly starting from a radially inner position in which they open the respectively assigned opening, wherein during this radial movement which is due to centripetal force, the cover elements pivot from the open position into the closed position as a result of the forced guidance via the coupling element. This radial movement occurs against the force of a restoring element, usually a spring which urges the respective cover element radially inwards again which, however, due to the high centripetal forces is overcome and pushed back. When the rotational speed of the wheel decreases again the movement is inverted. The cover elements open automatically via the force guiding coupling element when the decreasing centripetal forces allow the restoring element to cause the cover elements to move radially inward, and to assume their inner position.
A vehicle wheel of the type described above is known from EP 0 145 487 A2. In this wheel, a temperature-controlled actuating element is provided via which the cover elements can be actively moved into the open position in spite of higher driving speeds and radially outwardly closed cover elements when the temperature in the wheel interior is sufficiently high so that a cooling is strictly required. There, temperature controlled actuating elements for example shape memory alloys or bimetal elements are described which deform at sufficiently high temperatures and due the deformation exert a force on the assigned cover element in order to push the cover element against the high centripetal force to thereby push the cover element back via the positively guiding coupling element. This places high demands on the respective thermally controlled actuation elements, which thus have to have the corresponding working capacity.
A vehicle wheel which is improved in this regard is known from the subsequently published German patent application DE 10 2010 034 418.4. There, the positively guiding coupling element is supported against an elasticity on the wheel rim and/or on the cover element or has an integrated elasticity such that the force which is required for moving a cover element from the closed position into the open position is limited. This achieves, that the cover elements are pushed into the open position with a significantly lower force requirement because the required force is limited by the elasticity which is either integrated or situated in the bearing. This elasticity is for example realized by means of a helical spring or by means of rubber bearing rings.
A problem of vehicle wheels of the aforementioned type however is that undesired movements of the cover elements occur during the rotation of the wheel which result from a vertical excitation of the cover elements due to a vertical wheel movement. As described, the cover flaps are shifted between the positions along the pivot axis as a result of centripetal force and thereby are pivoted via the coupling element. When the vehicle drives on an uneven road, the wheel deflects in and out i.e., so that a wheel rim movement which has a vertical movement component is continuously established which in turn causes acceleration forces to act on the cover elements. It is assumed that the cover elements are all moved outwardly as a result of the given centripetal force and are pivoted into the closed position. Incase of a strong and fast deflection of the wheel, the road-proximate cover element is accelerated toward the wheel rim, it's position does not change because as assumed, it is already in the radially outer closed position. The opposing cover element however is accelerated toward the inside of the wheel rim i.e., at a sufficiently high acceleration it is moved from its radially outer closed position toward the inside of the wheel rim, associated with an opening of the aperture via the positively guiding coupling element. A sufficiently fast wheel rotation and relatively strong and high-frequent wheel movement thus results in the centripetal force superimposed accelerations or vibrations, which result in undesired movements of the cover elements. This is undesired from a mechanical point of view because high mechanical stresses on the pivoting coupling bearing result therefrom, and also because of disadvantageous acoustic effects which result from the continuous opening and closing sounds. This effect is also undesired from an aesthetics point of view.